Japanese Unexamined Patent Application Publication No. 2012-238808 (PTL 1) describes a GaN-based HFET. GaN used in this HFET has a large band gap, a high breakdown voltage, and a high electron drift velocity, and enables utilization of two-dimensional electron gas generated by a heterojunction. For example, when an AlGaN layer is stacked on an undoped GaN layer, two-dimensional electron gas is generated on a hetero-interface due to spontaneous polarization and piezoelectric polarization. HFETs that utilize the two-dimensional electron gas as a channel are known. Such an HFET may be applied to a power device for controlling a large current, and is advantageous in that the size thereof can be reduced compared to that of a Si-based HFET by exploiting the characteristics of the GaN-based HFET, such as low on-resistance.
In the above-described GaN-based HFET, a source wire and a drain wire are disposed in an active region of a device. A source electrode and a drain electrode are electrically connected to the source wire and the drain wire, respectively, via contact portions.